In recent years, reinforced environmental regulations have required that various fuel efficiency improvement devices or methods applied to vehicles have improved performance. Particularly, a need to meet the environmental regulations is further increased due to an increase in oil cost.
Such satisfaction of conditions may be realized by improving combustion characteristics of an engine. This realization technique includes, for example, a variable charge motion (hereinafter, referred to as “VCM”) system which satisfactorily mixes fuel and air in a cylinder by generating a tumble in intake air.
The VCM system includes a VCM motor, a VCM valve provided on an intake air passage of an intake manifold, a linkage link connecting a DC motor type VCM motor to the VCM valve, and an ECU for controlling the VCM motor. Hereinafter, the VCM is referred to as “link type VCM”.
When the link type VCM is operated, a position of the VCM motor is feedback controlled together with PID control by the ECU, movement of the VCM valve by the VCM motor varies the intake air passage of the intake manifold, and the tumble is generated in the intake air by a change in cross section of the intake air passage of the intake manifold, thereby allowing a mixture ratio of air and fuel to be further improved in the cylinder so as to improve combustion characteristics.
In particular, the ECU controls the VCM motor by a PWM (Pulse Width Modulation) duty linked with a change of an engine intake amount (engine mapping variable) when the PID control is performed, thereby most rapidly tracking a target position of the VCM motor.
However, the VCM motor has a response speed of about 150 m/sec and is controlled so as to reach a target by motor duty reduction occurring after reaching a target position by the PWM duty of differential control (D) of PID having integral/differential concepts. Thus, signal vibration may be caused by noise generated when the VCM motor does not rapidly reach the target position.
In particular, since the VCM motor is connected to the VCM valve by the link, the VCM motor is influenced by back pressure of intake air flowing in the intake air passage of the intake manifold. For this reason, when the VCM motor does not rapidly reach the target after reaching the target position, noise vibration of duty reduction signals may be caused.
Therefore, when the differential control PWM duty for improving the response speed is improperly set, the VCM motor may be seriously influenced by disturbance or noise. Particularly, when the VCM motor is used at a temperature exceeding a critical temperature (about 200° C. or more) by excessive use of the PWM duty, coils of the VCM motor may be damaged.